This invention relates generally to optical peephole devices, and more particularly to an optical device which is insertable in the peephole of a thick-walled chamber such as a bank safe, making it possible to inconspicuously but almost fully inspect the interior thereof.
Devices are known, commonly called optical peepholes, which make it possible for an observer located behind a door to almost entirely perceive those objects which are present on a stairway landing, provided, of course, that these objects are sufficiently illuminated. Such optical peephole devices are generally constituted by an optical doublet comprising either a pair of thick-edged lenses, or a meniscus and a thick-edged lens. This doublet forms a strongly divergent optical system and, depending on certain arrangements or on the diopters of its optical elements, it affords a virtual image of the various objects located on the stair landing. Usually this virtual image is observed with the aid of a convergent lens which at the same time allows some degree of magnification of the image and accommodation to the eye.
One can readily appreciate that a peephole optical device for this purpose cannot be very long, otherwise it would produce an image having very poor luminosity. Thus an optical peephole device of the above-described type is not applicable to observations through walls having a thickness greater than about ten centimeters.
To ensure the security of certain chambers or enclosures, such as strongboxes, safes or bank vaults, one must be able to discreetly carry out observations at regular intervals from the exterior of the chamber. To facilitate such observation, it has heretofore been proposed that television cameras be placed at several points within the chamber, permitting the field of view of the cameras to be displayed on television screens. Such a closed-circuit television system, although very effective, is also very expensive, which is a distinct practical drawback.
It has also been proposed that the interior of the enclosure be inspected with the aid of an endoscope of the medical type, or by a periscope. A serious drawback of both such devices is that their field of view is quite limited (for example, to a solid angle of 30.degree. to 60.degree.). As a consequence, it is necessary to make these narrow angle devices turn on their axes to sweep the entire field. This renders the observation procedure conspicuous, which is undesirable. The fact that such devices must be projected somewhat into the interior of the enclosure also causes them to be conspicuous and more costly.